Supplementary Material for: Ectopic atrial beats may cause a ZigZag pattern at intrapartum recording of the fetal heart rate using fetal scalp electrode

Novel Insights
Continuous intrapartum fetal heart rate assessment by fetal scalp electrode may record arrythmias like recurrent atrial ectopic beats and depict an increased fetal heart rate variability mimicking a ZigZag pattern.
Introduction
Fetal scalp electrode (FSE) is considered the gold standard for the intrapartum monitoring of the fetal heart rate (FHR) being associated with the lowest rate of signal loss and artifacts including the recording of the maternal heart rate. FSE acquires a fetal electrocardiogram and evaluates the time intervals between successive R waves. As such, it allows the recording of the beat-to-beat fluctuation of the FHR. However, due to the precise estimation of the inter-beat interval, FSE may also demonstrate recurrent atrial ectopic beats and register a highly oscillatory FHR pattern mimicking a saltatory or ZigZag appearance.
Case Presentation
We herein describe a case of intrapartum supraventricular ectopic beats leading to the recording of a saltatory appearance of the FHR that could be demonstrated using FSE only and precluded a reliable assessment of intrapartum fetal oxygenation. Transabdominal gray-scale and M-mode ultrasound assessment of the fetal heart documented supraventricular ectopic beats recurring in 1 out of 10-12 beats, thus supporting the hypothesis that the abnormal FHR pattern on the CTG trace was secondary to fetal arrhythmia and not to rapidly evolving fetal hypoxia.
Conclusion
In supraventricular fetal arrhythmia the use of FSE for continuous intrapartum FHR monitoring differently from external ultrasound transducer may capture a highly variable CTG pattern which is caused by the registration of the ectopic atrial beats and not by a rapidly evolving hypoxia.